thallous adjective. ['Ɵalǝs] L19.
[from THALLIUM + -OUS.]
Chemistry. Of or containing thallium, esp. in its monovalent state.
thallous oxide thallium monoxide, Tl₂O, a black powder used in glass-making etc.
Also
■ thallious ['Ɵalɪǝs] adjective (now rare) M19.

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